In the automotive industry, numerous efforts have been undertaken over the years to restrict or reduce emissions resulting from the internal combustion process. In particular, emissions of NOx and particulate matters (PM) produced by a diesel engine have been targeted for reduction. One technique that has been contemplated for use, particularly, as a system for reducing NOx is the Exhaust Gas Recirculation (EGR) system.
A known process uses the measured pressures of a flow through a restriction, such as a venturi, throttle, or orifice, to calculate the mass flow of a media through a pipe. Common applications of this process are within the exhaust gas recirculation loop or throttle system in engines. This is typically performed using either: two discrete absolute pressure sensors on opposite sides of the restriction; or a differential pressure sensor across the restriction with a separate absolute pressure sensor on one side. Both of these configurations lead to inherent error in the mass flow calculation by compounding the errors between the two sensors.
Referring now to FIG. 1, there is illustrated a conventional EGR loop design or EGR system for use with an exemplary internal combustion engine, for example a diesel engine. As discussed further below such an EGR system embodies a differential pressure sensor across the restriction with a separate absolute pressure sensor on one side (i.e., the upstream side) for purposes of determining the mass flow rate of the EGR gases. In such an EGR system a part of the exhaust gas is returned to the intake side of the engine to lower the oxygen concentration of the intake gas going to the engine cylinders as well as to reduce the temperature within the cylinders so as to thereby reduce the production of NOx. Also shown is an exemplary fuel delivery system and other mechanism(s) provided for dealing with undesirable exhaust products such as for example, a diesel particulate filter (DPF). The illustrated intake of the exemplary engine also includes a turbine and compressor which are used to turbocharge the intake air being supplied to the engine.
In such an EGR system, it is important to control the return quantity from the exhaust side to the intake side. As indicated above, to measure the EGR mass flow rate, it is customary to dispose an orifice or Venturi (e.g., restriction venturi) inside the EGR pipe and to detect the difference in pressure of the exhaust gas between portions ahead of and behind the orifice or Venturi. The internal construction of the EGR pipe at the connection portion with such a pressure sensor includes an upstream side pressure discharge path for discharging an upstream side pressure P1 of the orifice and a downstream side pressure discharge path for discharging a downstream side pressure P2 of the orifice. As also indicated above, to calculate the mass flow using such a restriction venturi, one measures the following factors the high side absolute pressure, the differential pressure across the venturi and the temperature of the recirculating exhaust temperature or EGR temperature.
Referring now to FIG. 2, there is shown a conventional arrangement for such an EGR loop/system that includes an absolute pressure transmitter (APT) that measure and outputs a signal(s) of the high side absolute pressure, a temperature transmitter (TEMP) that measures and outputs a signal(s) of the EGR temperature; and a module (HCM) that measures and provides an output representative of the differential pressure (high pressure-low pressure) developed across the restriction venturi. As further illustration of such a system and module, reference is herein made to U.S. Pat. No. 7,578,194 (which is commonly owned with the present invention), the teachings of which are incorporated herein by reference. See also the following discussion regarding same.
These outputs representative of the absolute pressure, EGR temperature and differential pressure are provided to the engine control unit or ECU (a unit embodying a digital processing device/mechanism such as a microprocessor, an ASIC, a digital signal processor or the like) which embodies in hardware and/or software a mechanism (e.g., algorithm) for determining the mass flow rate of the exhaust gasses flowing through the EGR pipe (e.g., venturi). Using this information, the ECU can then adjust the flow of exhaust gas being returned to the intake side to an appropriate value. Such an ECU also can be configured and arranged so as to control the operation of the engine or other components of the motor vehicle relating to the engine or engine control (e.g., automatic transmission).
In addition there is found in U.S. Pat. No. 7,578,194, a differential fluid pressure sensor apparatus that includes a housing to which is mounted a sense element module. The sense element module has first and second diaphragm mounting surfaces facing outwardly in a common direction, and a passageway formed in the module and extending between and forming an opening inside each respective diaphragm mounting surface. Also, a respective flexible metal diaphragm is mounted on each diaphragm mounting surface over each opening, and a pressure responsive sense element is disposed in one of the openings of the passageway. A non-compressible fluid fills the passageway and engages the diaphragms and seals therein. Also included are electrical signal conditioning circuitry operatively connected to the pressure responsive sense element, and first and second fluid pressure connection means for presenting respective high and low fluid pressure to the flexible diaphragms for monitoring. As indicated above, such an apparatus is configured for sensing only differential pressure.
Also, it is provided that such solid state pressure sense elements (e.g., piezo resistive pressure sense elements) used for such pressure sensing applications are isolated from the media being sensed by a flexible metal diaphragm robust to the media to protect such sense elements from the harsh makeup of the exhaust gasses. An incompressible fluid or non-compressible fluid, typically silicone oil, is located between the sense element and the diaphragm and is used to transfer pressure from the diaphragm to the sense element. In this way, the sense element can sense and measure the pressure of the media.
There is found in U.S. Pat. No. 7,197,936 a pressure difference (relative pressure) detection type pressure sensor that is fluidly coupled across an orifice disposed in an exhaust gas recirculation (EGR) pipe to detect a pressure difference between portions ahead or upstream of the orifice (high pressure) and behind or downstream of the orifice (low pressure). More particularly, the EGR pipe is configured so as to include an upstream pressure discharge path that provides an upstream side pressure of the orifice and a downstream pressure discharge path that provides a downstream side pressure of the orifice. The upstream and downstream pressure discharge paths are fluidly coupled to the pressure sensor so the pressure sensor can detect or sense the differential pressure. This patent also suggests that the described differential pressure sensor can be applied as a sensor for detecting an intake pressure inside an intake pipe of an engine or an exhaust pressure inside and exhaust pipe. It is further suggested that the sensor also can be disposed in an exhaust pipe to detect a pressure loss of a diesel particulate filter (DPF).
The discussions for the following identified US patents and US patent application Publication illustrate some common themes: differential and absolute sense elements located within one MEMS die; sensors outputting differential and absolute pressure measurements utilizing two absolute sense elements; sensors outputting differential and two absolute pressure measurements utilizing two absolute sense elements; and a system outputting differential and absolute pressure measurements utilizing one differential and one absolute capacitive based deformation sensors mounted to diaphragm plates.
There is found in U.S. Pat. No. 4,131,088 a multiple function pressure sensor for use in combination with an electronic fuel injection system for an internal combustion engine. Such a pressure sensor includes two pressure sensitive elements in a single housing which generate signals indicative of the absolute pressure in the engine's intake manifold and the absolute value of the ambient or atmospheric pressure. Also included is electronic circuitry that subtracts the value of the engine's manifold pressure from the value of the atmospheric pressure and generates a third pressure signal indicative of the difference between the manifold pressure and atmospheric pressure. These three pressure signals are utilized in the electronic fuel injection system for computing the fuel requirements of the engine under various operating conditions.
There is found in U.S. Pat. No. 5,259,248 an integrated multi-sensor or composite sensor which is used in a pressure and differential pressure transmitter for detecting a flow (or the quantity of flow) or a pressure in a chemical plant or the like and also relates to an intelligent differential pressure transmitter and a plant system which use such an integrated multi-sensor. Such an integrated multi-sensor includes a pair of static pressure gages that are formed on a static pressure detecting diaphragm and another pair of static pressure gages that are formed at positions on a fixed portion which are near to the center of a differential pressure detecting diaphragm. By constructing a static pressure sensor so as to form a bridge circuit, a static pressure value free of the influence of a differential pressure can be detected, thereby making it possible to determine an accurate differential and static pressure.
There is found in U.S. Pat. No. 6,473,711 an interchangeable differential, absolute and gage type of pressure transmitter. Such a pressure transmitter includes first and second absolute pressure sensors that receive process pressures from corresponding first and second process inlets. A transmitter circuit coupled to the first and second absolute pressure sensors generates a differential pressure type output. Such a pressure transmitter also includes a third absolute pressure sensor coupled to the circuit, which receives atmospheric pressure from a third inlet. The transmitter circuit generates a second type of transmitter output that can be a gage or absolute pressure type. It is further provided that the transmitter circuit couples to the three absolute pressure sensors, and the transmitter circuit generates differential and non-differential type outputs, such that the transmitter is interchangeably adaptable between differential and non-differential installations.
There is found in U.S. Pat. No. 7,073,375 sensor systems and methods. Such a system embodies an exhaust back pressure sensor using an absolute micro-machined pressure sense die. It is further provided that the core technology to such an exhaust back pressure sensor system is the absolute pressure sensor die. Such a system also includes a sensor's electronic circuit that can incorporate one or more ASICs that process(es) and output(s) the signal for both absolute and differential measurements. Such a sensor can be adapted for use in exhaust gas re-circulation (EGR) systems utilized with automotive gasoline engines. Such a sensor also can be utilized for measuring differential pressure across diesel particular filters and/or applications in which differential pressure is required for system control and/or monitoring purposes. The described absolute pressure sensor can therefore sense the exhaust pressure on automotive engines and other mechanical and/or electromechanical devices and machines.
There is found in U.S. Pat. No. 7,270,011 a micromechanical sensor for measuring at least a first pressure of a first medium and more particularly is a combined absolute-pressure and relative-pressure sensor. Such a micromechanical sensor has at least one substrate having at least two sensor elements. The substrate has at least a first sensor element for measuring an absolute-pres sure variable of the first medium and a second sensor element for measuring a relative-pressure variable of the first medium.
There is found in U.S. Pat. No. 7,743,662 a low differential pressure transducer. Such a pressure transducer includes an H-shaped header having a front and back section, where the front and back sections are of equal diameter and are circular. Each front and back section has a depression with a first and second diaphragm covering the respective depression. Each diaphragm is of equal size and the depressions communicate one with the other via a central channel in the central arm of the H. A pressure sensor communicates with the channel, where the pressure sensor responds to a first pressure applied to the first diaphragm and a second pressure applied to the second diaphragm. The pressure sensor produces an output equal to the difference in the pressure.
There is found in U.S. Pat. No. 8,132,464 a differential pressure transmitter with complimentary dual absolute pressure sensors. It is more particularly provided that such a process variable transmitter for measuring a pressure of a process fluid includes a process coupling having a first port configured to couple to a first process pressure and a second port configured to couple to a second process pressure. A differential pressure sensor is coupled to the first and second ports and provides an output related to a differential pressure between the first pressure and the second pressure. First and second pressure sensors couple to the respective first and second ports and provide outputs related to the first and second pressures. Transmitter circuitry is configured to provide a transmitter output based upon the output from the differential pressure sensor and/or the first and/or second pressure sensors.
There is found in U.S. Pat. No. 8,171,800 a differential pressure sensor using dual backside absolute pressure sensing. A MEMS differential pressure sensing element is provided by two separate silicon dies attached to opposite sides of a silicon or glass spacer, the sides of which are recessed and the recesses formed therein at least partially evacuated. The dies are attached to the spacer using silicon-to-silicon bonding provided in part by silicon oxide layers if a silicon spacer is used. The dies can be also attached to the spacer using anodic bonding if a glass spacer is used.
There is found in U.S. Pat. No. 8,215,176 a pressure sensor for harsh media sensing and flexible packaging; more particularly, a MEMS pressure sensing elements that provide a way for a harsh media absolute pressure sensing and eliminating the negative effects caused by the gel used in the prior art. Such a pressure sensor uses vertical conductive vias to electrically connect the enclosed circuit to the outside, and uses a fusion bond method to attach a cap with the embedded conductive vias over a device die having a circuit for example a piezo resistive Wheatstone bridge to sense pressure. Such a sensor includes a two-pocket housing structure and uses a surface mounting method to attach a sensing element into one pocket by a ball grid array (BGA), and a single pocket structure using conventional die attach and wire bonding. Both can be used for harsh media pressure sensing but without the negative effects caused by the gel in prior art. It is further provided that the sensor is arranged so that diaphragm deflections are caused by a pressure to be measured, where such an embodiment is referred to as an absolute pressure sensor. In an alternate embodiment, the sensor can be configured so it functions as a differential pressure sensor.
There is found in U.S. Pat. No. 8,234,927 a differential pressure sensor with line pressure measurement. More particularly, there is found a pressure sensor assembly for sensing a pressure of a process fluid, such an assembly including a sensor body having a cavity formed therein and first and second openings to the cavity configured to apply first and second pressures. A diaphragm in the cavity separates the first opening from the second opening and is configured to deflect in response to a differential pressure between the first pressure and the second pressure. A capacitance based deformation sensor is provided and configured to sense deformation of the sensor body in response to a line pressure applied to the sensor body.
There is found in U.S. Publication No. 2014/0165735 a differential pressure transducer configured for matching back pressures on differential oil-filled diaphragms. More particularly, such a differential pressure transducer includes first and second diaphragms of different configurations, i.e., different diameters and/or thicknesses. The pressure transducer provides more versatility over prior art designs as the diaphragms can be of different configurations yet still maintain substantially similar back pressures. Therefore, the errors commonly associated with back pressures are eliminated because the back pressures from the diaphragms ultimately cancel out in the sensor's differential pressure measurement.
There is found in WO1995008758 a two-wire transmitter that senses differential pressure, absolute pressure, and process temperature of a process fluid. The information can be used to provide an output representative of mass flow through a pipe. The transmitter has an electronics module housing attached to a sensor module housing.
There is found in WO2005052535 a method and apparatus that integrates differential pressure measurements and absolute pressure measurements to provide virtual absolute pressure measurements over a wide range of pressures on a single integrated scale. To achieve the foregoing objects the method and apparatus for measuring absolute pressure in a chamber includes determining a correlation factor between absolute and differential pressure measurements taken simultaneously at a pressure where the absolute pressure in the chamber can be measured accurately, and adjusting differential pressure measurements with the correlation factor to provide virtual absolute pressure measurements
It thus would be desirable to provide a new system, apparatus and methods for determining absolute pressure and differential pressure using two pressure sense elements. It would be particularly desirable to provide such system, apparatus and methods which can be used in combination with other devices to determine mass flow rate of exhaust gas in an EGR application and/or mass flow rate of the intake air. Such systems and apparatus preferably would result in a simpler or less complicated construction as compared to prior art systems and apparatus while maintaining an accuracy comparable to prior art systems/apparatuses. Also such systems and apparatus preferably reduces part count and installation costs as compared to prior art systems/apparatuses particularly when one considers the cost savings associated with the number of engines being produced.